If you calculate the time they have spent with you and the time they'll put in until the closing, what are their hourly rates?
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Your question should be directed at the agents and brokerage company involved as there is not one person in this forum that can give you the answer as to what they will do. Mac is right - what bargining power do you have??? Not to buy the house, not to sell your home, use a different office? You have signed contracts with them already?
With that being said, there is nothing preventing you from inquiring about a variable commission rate, but the decision to agree to it or not, is up to the Broker/Owner, not the individual Agents.
Best of luck!